Internal combustion (IC) engines have been the prime mover for more than a century. Nevertheless there remain opportunities for continuous improvement in key engine attributes such as specific power output, fuel economy, and exhaust emissions. The present invention represents an important discovery in the IC engine technologies to improve the above-mentioned attributes. The compression ignition direct injection (CIDI) diesel engine burns 30% to 50% less fuel as compared to a similar size homogeneous charge spark ignition (HCSI) gasoline engine, but with the disadvantages of increased nitric oxide and particulate matter emissions, start-ability, and specific power output. On the other hand HCSI gasoline engines offer the advantages of lower nitric oxide and particulate matter emissions, improved start-ability, and specific power output, but with poor fuel economy and drive-ability. A hybrid of CIDI and HCSI processes such as homogeneous charge compression ignition (HCCI) or premixed charge compression ignition (PCCI) has the potential to be highly efficient and to produce very low exhaust emissions. Nevertheless many major technical barriers must be overcome to achieve the above objectives. Significant challenges include controlling ignition timing and burn rate over all engine operating conditions, poor cold starts and transient response, and high hydrocarbons and carbon mono-oxide emissions.
For the compression ignition operations such as CIDI, HCCI, and PCCI, the formation of active radical (i.e., reactive chemical compounds such as H, OH, and HO2.) in the main fuel charge leads to ignition. The pre-ignition process is controlled mainly by hydrogen peroxide decomposition. Hydrogen peroxide decomposes into two OH radicals that are very efficient at attacking the fuel and releasing energy. Although the amount of energy liberated is at first too small to be considered ignition, these low temperature reactions quickly drive the mixture up to the 800-1,100 deg K necessary for H2O2 decomposition and main ignition, depending on the type of fuel used. The process is dominated by the kinetics of local chemical reactions. A small temperature difference inside the cylinder has a considerable effect on the ignition timing of the main fuel charge due to the sensitivity of chemical kinetics to temperature. As a result, heat transfer and mixing are important in forming the condition of the charge prior to ignition. The quality of the mixture and the fuel air ratio supplied to each cylinder should be uniform from cylinder-to-cylinder and cycle-to-cycle. However, due to the transient nature of the IC engines with continuous changing of engine operating and boundary conditions, experts in the field have been unable to control compression ignition timing by directly managing the conditions and composition of the main fuel charge through the whole cycle of intake and compression strokes. The ignition timing of a conventional diesel engine is controlled indirectly by the injection timing of the main fuel charge. That is, the start of ignition timing is equal to the start of injection timing plus ignition delay. Unless the ignition delay can be fixed or made to be near zero, the start of ignition cannot be controlled completely by the injection timing of the main fuel charge. Furthermore, for a Homogeneous Charge Compression Ignition (HCCI) or Premixed Charge Compression Ignition (PCCI) engine there is no in-cylinder direct injection timing of the main fuel charge to vary. The main fuel charge is well mixed before entering into the combustion chamber and/or before the beginning of compression stroke. Uncontrolled ignition timing leads to an uncontrolled combustion and excessive engine knocking.
Many attempts to control the compression ignition timing of a conventional direct injection diesel engine by managing directly the conditions and composition of the main charge have been unsuccessful. Some attempts were designed to improve the fuel atomization and mixture preparation processes through the use of an auxiliary compressed air supply without addressing and controlling the appropriate conditions of temperatures and pressures histories (U.S. Pat. Nos. 4,846,114 and 5,119,792). Others were to heat up the fuel spray to improve the pre-ignition process through the use of electrical heating elements but at the expense of operational safety, very high unburned hydrocarbon emissions, and compromising the main fuel charge injection characteristics (see U.S. Pat. Nos. 4,603,667; 4,787,349; 4,926,819; 6,722,339; 6,289,869, and 6,378,485). All such systems are simply not rapid and flexible enough to achieve the right conditions of temperature, pressure and mixture composition histories for a controlled ignition process. In addition, a compromise on the main injection characteristics can lead to a poor main combustion process and to very high smoke.